1. Field of the Invention
The present invention relates to a sealing method applicable to a packaging bag in which the opening area of the bag that contains packaged matter is ultrasonically sealed and further relates to a packaging bag which is sealed by such a method.
2. Prior Art
Opening areas of packaging bags that are filled with, for instance, liquids, powders, etc. are sealed in several ways. In one method, sealing is performed by holding the bag together with the content (the packaged matter) with a sealing tool in a horizontal attitude in the position where the content is present (such position being where the packaged matter adheres to the inner surface of the bag). This method (which is called “sealing in liquid” in cases where the packaged matter is a liquid substance, see the prior art below) is advantageous in which it leaves as little air as possible inside the sealed space of the bag after sealing.
However, if the method above is accomplished by general heat-sealing (heat-sealing that uses heating plate, or impulse sealing), a portion of the packaged matter adhering to the inner surface of the bag is caused to bite into the sealed area (this is called a “bite-in seal”), thus causing an incomplete sealing of the opening area. In view of this, ultrasonic sealing is utilized ordinarily. With the ultrasonic sealing, the packaged matter adhering to the inner surface of the bag is separated upward and downward, and then this area is sealed; accordingly, the problem of a “bite-in seal” is avoided.
However, the ultrasonic sealing has problems. For instance, in cases where the content is a liquid substance, if the ultrasonic sealing is performed in the position where the liquid substance adheres to the opening area, the area beneath the ultrasonically sealed area 1, as seen from FIG. 4, forms a sealed space that contains liquid substance 2 alone, with air excluded, and a liquid substance 2a that is separated by the ultrasonically sealed area 1 adheres to the inner surface of the bag above the ultrasonically sealed area 1. Since this liquid substance 2a is present outside the sealed space, the liquid substance 2a subsequently spills out of the bag mouth and contaminates the surface of the bag. Even if the liquid substance 2a does not spill, the external appearance of the product is deteriorated; and there are also problems in terms of hygiene in cases where the packaged matter is a foodstuff.
This problem can be overcome by way of, as shown in, for instance, Japanese Patent No. 3079185, applying a broad heat-sealing so that it overlaps with the ultrasonically sealed area 1 (which ordinarily has a width of 2 to 3 mm) after executing the ultrasonic sealing. However, if this is done, the liquid substance is volatilized during heat-sealing as shown in FIG. 5, and this volatilized portion of the liquid substance is sealed in (i.e., the upper portion where no liquid substance is present is fused first, so that a portion of the vapor is sealed in). Consequently, numerous gas bubbles 4 enter the heat-sealed area 3, and the external appearance of the product is damaged; and in some cases, a portion of the liquid substance is squeezed out of the bag mouth “as is” as a result of being pressed by the press-holding members of the heat-sealing plates, etc. This liquid substance contacts the press-holding members of the heating plates, etc. and evaporates, thus contaminating the pressing surfaces of the press-holding members. Liquid substance that is not completely evaporated contaminates the bag surfaces.
In cases where the packaged matter is not a liquid substance, the problem of gas bubbles, etc. can be avoided; however, the packaged matter is enclosed across the heat-sealed area, and the external appearance of the product is likewise damaged.